Ignition coils are components that use the coupling between a primary winding and a secondary winding to transform relatively low voltages from the battery into high voltages that are supplied to the spark plugs in vehicle gasoline engines. The spark plugs start the internal combustion process that drives the rods and hence, crankshaft and axles. In older systems, a single ignition coil is provided, and a distributor sends the pulses from the coil through respective high voltage spark plug wires to the spark plugs in the cylinders in accordance with a timing that is established by the distributor.
In relatively modern engines, an engine can have several ignition coils, one for each cylinder or for each pair of cylinders, thereby advantageously eliminating the need for distributors and high voltage wires and also providing more precise control of the engine timing. One example of such an ignition coil system is set forth in U.S. Pat. No. 6,556,118, owned by the present assignee and incorporated herein by reference.
To provide a magnetic return path to the primary core around which the primary windings are wound, steel shields have been provided that surround the inside or outside of the case which holds the core. The primary core typically is centrally disposed in a secondary winding spool around which the secondary windings are wound, and the case holds the primary/secondary assembly. Such a shield, which also serves to direct flux to a main air gap that is associated with pole pieces, is described in U.S. Pat. No. 5,015,982, incorporated herein by reference.